Oxide Layer Structure

Pb and Tl electrodeposited onto Ag were unstable at open circuit in a variety of electrolytes tested representing various anions (C104 , F , CP, Br , I-) and alkaline, neutral, or acid pH [49]. Ordered layers of PbO or T10H were formed during evacuation. Oxide layer structures were determined in each case and were found to vary with the electrolyte anion. 

In a recent paper by Bolzan and Arvia, the oxygen evolution reaction (OER) was studied on different types of oxide-coated Pt electrodes in 1 mol dm H2SO4. The various oxide layers were obtained by various potential cychng and by galvanostatic oxidation. The experimental results were interpreted in terms of different oxide layer structure on the basis of the assumptions ... 

Figure 8 SNMS depth profile of an insulating oxidic layer structure (65nm TiOa/SOnm Si02/65nm Ti02/float glass). Analysis with charge compensated external bombardment mode with 5keV Kr+.

The major artifacts contributing to uncertainties in PDCE results stem from effects caused by bombardment of nonideal specimens, particularly thick specimens. The ideal thick specimen would be a homogeneous, smooth electrical conductor that does not change during bombardment. Except for rather simple, well-defined layered structures (e.g., surface oxide layers), specimens having compositional variations with depth yield spectra whose analyses can have large inaccuracies. 

Feitknecht has examined the corrosion products of zinc in sodium chloride solutions in detail. The compound on the inactive areas was found to be mainly zinc oxide. When the concentration of sodium chloride was greater than 0-1 M, basic zinc chlorides were found on the corroded parts. At lower concentrations a loose powdery form of a crystalline zinc hydroxide appeared. A close examination of the corroded areas revealed craters which appeared to contain alternate layers and concentric rings of basic chlorides and hydroxides. Two basic zinc chlorides were identified, namely 6Zn(OH)2 -ZnClj and 4Zn(OH)2 ZnCl. These basic salts, and the crystalline zinc hydroxides, were found to have layer structures similar in general to the layer structure attributed to the basic zinc carbonate which forms dense adherent films and appears to play such an important role in the corrosion resistance of zinc against the atmosphere. The presence of different reaction products in the actual corroded areas leads to the view that, in addition to action between the major anodic and cathodic areas as a whole, there is also a local interaction between smaller anodic and cathodic elements. 

In 1929 Pfeil" published a most interesting account of the way layered structures form and the manner in which they influence oxidation rates. From detailed studies of the growth and composition of scales he was able to show clearly how the formation of barrier layers reduced scale formation by hindering outward diffusion of iron through the scale. Naturally, this work had to be largely based on the study of scales of sufficient thickness so that the mechanism of the early stages of oxidation could not be studied in this way. Pfeil analysed the outer, middle and inner layers of scales formed... 

Figure 8. Schematic drawing of the layered manganese oxides. The structure consists of a stacking of empty and Mn(III, IV)-filled layers of edge-sharing octahedra.

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